In a typical radio data communication system having one or more host computers and multiple RF terminals, communication between a host computer and an RF terminal is provided by one or more base stations. Depending upon the application and the operating conditions, a large number of these base stations may be required to adequately serve the system. For example, a radio data communication system installed in a large factory may require dozens of base stations in order to cover the entire factory floor.
In earlier RF (Radio Frequency) data communication systems, the base stations were typically connected directly to a host computer through multi-dropped connections to an Ethernet communication line. To communicate between an RF terminal and a host computer, in such a system, the RF terminal sends data to a base station and the base station passes the data directly to the host computer. Communicating with a host computer through a base station in this manner is commonly known as hopping. These earlier RF data communication systems used a single-hop method of communication.
In order to cover a larger area with an RF data communication system and to take advantage of the deregulation of the spread-spectrum radio frequencies, later-developed RF data communication systems are organized into layers of base stations. As in earlier RF data communications systems, a typical system includes multiple base stations which communicate directly with the RF terminals and the host computer. In addition, the system also includes intermediate stations that communicate with the RF terminals, the multiple base stations, and other intermediate stations. In such a system, communication from an RF terminal to a host computer may be achieved, for example, by having the RF terminal send data to an intermediate station, the intermediate station send the data to a base station, and the base station send the data directly to the host computer. Communicating with a host computer through more than one station is commonly known as a multiple-hop communication system.
Difficulties often arise in maintaining the integrity of such multiple-hop RF data communication systems. The system must be able to handle both wireless and hard-wired station connections, efficient dynamic routing of data information, RF terminal mobility, and interference from many different sources.
The present invention solves many of the problems inherent in a multiple-hop data communication system. The present invention comprises an RF Local-Area Network capable of efficient and dynamic handling of data by routing communications between the RF Terminals and the host computer through a network of intermediate base stations.
In one embodiment of the present invention, the RF data communication system contains one or more host computers and multiple gateways, bridges, and RF terminals. Gateways are used to pass messages to and from a host computer and the RF Network. A host port is used to provide a link between the gateway and the host computer. In addition, gateways may include bridging functions and may pass information from one RF terminal to another. Bridges are intermediate relay nodes which repeat data messages. Bridges can repeat data to and from bridges, gateways and RF terminals and are used to extend the range of the gateways.
The RF terminals are attached logically to the host computer and use a network formed by a gateway and the bridges to communicate with the host computer. To set up the network, an optimal configuration for conducting network communication spanning tree is created to control the flow of data communication. To aid understanding by providing a more visual description, this configuration is referred to hereafter as a xe2x80x9cspanning treexe2x80x9d or xe2x80x9coptimal spanning treexe2x80x9d.
Specifically, root of the spanning tree are the gateways; the branches are the bridges; and non-bridging stations, such as RF terminals, are the leaves of the tree. Data are sent along the branches of the newly created optimal spanning tree. Nodes in the network use a backward learning technique to route packets along the correct branches.
One object of the present invention is to route data efficiently, dynamically, and without looping. Another object of the present invention is to make the routing of the data transparent to the RF terminals. The RF terminals, transmitting data intended for the host computer, are unaffected by the means ultimately used by the RF Network to deliver their data.
It is a further object of the present invention for the network to be capable of handling RF terminal mobility and lost nodes with minimal impact on the entire RF data communication system.